An automobile headlamp conventionally is capable of changing between two modes: a high beam mode (traveling mode) with a light distribution pattern for brightly illuminating a far distance ahead which is suitable for country driving, and a basic mode (passing mode) with a light distribution pattern for illuminating an area in front of a host vehicle while suppressing glare with respect to another vehicle in cases of city driving where there is another vehicle such as an oncoming vehicle or a preceding vehicle. However, various light distribution modes have been proposed in recent year for achieving suitable illumination for every travel condition of the automobile. Examples include a motorway mode for increasing a distant illumination intensity ahead during high speed travel of the host vehicle within a range that does not interfere with the driver of an oncoming vehicle, and a wet road mode that reduces interference with the driver of an oncoming vehicle, which is due to light radiated directly in front of the host vehicle during travel in rainy weather that reflects off the road surface.
In order for the headlamp to change between the light distribution patterns of the high beam mode, the basic mode, the motorway mode, and the wet road mode, multiple shades having different light-blocking patterns conventionally are provided for partially shading light emitted from a light source of a lamp. A target light distribution pattern then is obtained by selecting and changing between these shades. However, it is difficult to obtain light distribution patterns suitable for travel conditions by simply changing between the shades alone. Therefore, changing the shade and varying an illumination optical axis of the lamp at the same time also has been proposed. For example, Japanese Patent Laid-Open Application (Kokai) No. 2006-221882 proposes a headlamp in which a lamp reflector is vertically tiltable and a shade in the lamp is changeable. Tilting the shade varies a shaded region of light emitted from a lamp light source. According to the foregoing patent application, a light distribution pattern can be varied slightly by tilting the shade to change the shaded region, and by tilting the reflector to vary an illumination optical axis. Thus, a light distribution pattern suitable for a particular travel condition can be obtained.
In the foregoing patent application, the reflector is vertically tilted to vary the illumination optical axis in the vertical direction. Therefore, the light intensity distribution of the light distribution pattern is only changed in the longitudinal direction when looking at the road surface from the vertical direction, i.e., when looking at the road surface ahead from the host vehicle. As a consequence, a brightest light intensity region of the light intensity distribution may be blocked when the shade is changed, which means that a light distribution suitable for a particular travel condition may not be obtained. For example, FIG. 3(a) shows a light distribution region of the lamp when light is not blocked by the shade (i.e., a light distribution pattern for a high beam mode), and FIG. 3(b) shows a light distribution pattern for a basic mode when the light distribution region is partially blocked by the shade. Ax is an axis representing a straight travel direction of the host vehicle (hereinafter referred to as a straight travel axis), and V and H are a vertical line and a horizontal line that pass through the straight travel axis Ax, respectively. In addition, the illumination region is indicated by light intensity contour lines in order to illustrate the distribution of light intensity schematically. The center is a high light intensity region. In the basic mode, the central high light intensity region of the illumination region is shaded so that the driver of an oncoming vehicle is not dazzled. In contrast to the light intensity distribution, in order to set the motorway mode, which illuminates a far distance ahead of a host vehicle lane ML at a high light intensity, the shade is used to change the shaded region so that the high light intensity region is not partially blocked. However, part of the high light intensity region overlaps with an oncoming vehicle lane OL as shown in FIG. 3(c), which may dazzle the driver of the oncoming vehicle as well as a preceding vehicle. Accordingly, when there is an oncoming vehicle or a preceding vehicle present during high speed travel, illumination must be changed and set to that of the basic mode as shown in FIG. 3(b), which results in inadequate brightness at a far distance ahead of the host vehicle lane ML. In the foregoing patent application, the headlamp can rotate laterally. This configuration is used so that the headlamp can follow and deflect in accordance with steering of the automobile; however, the light distribution pattern is not deflected during a straight travel condition of the host vehicle.
In the foregoing patent application, light distribution according to the wet road mode cannot readily be achieved. To achieve light distribution according to the wet road mode, it is necessary to shade reflected light headed toward an oncoming vehicle or a preceding vehicle on the road surface in the directly forward region of the host vehicle as indicated by a broken line WA in FIG. 3(c). To this end, a shade that blocks a lower region must be provided in addition to a shade that blocks an upper region of the illumination region of the lamp. In addition, a structure is needed to change between blocking and not blocking light using this shade. However, this results in a more complex lamp structure. Costs and other factors, make the realization of a headlamp compatible with the above wet road mode difficult.